A significant problem with telephone headset adapters is that they have to be configured to match the host phone to which they will be attached. This configuration involves making sure that the cable wiring of the adapter matches that of the host phone handset jack, ensuring an appropriate transmit signal gain applied to a transmit signal received from a headset microphone, and ensuring an appropriate receive signal gain applied to a receive signal to be output at a headset speaker. Certain settings may be required to obtain the best signal quality and meet network regulatory requirements.
The electrical connection to the host phone handset jack typically includes four wires, two of which are connected to a receive circuit and two of which are connected to a transmit circuit. In order for the headset adapter to process and transfer the transmit signal received from a headset microphone, the headset adapter transmit lines must be matched with the two wires of the host phone handset jack corresponding to the host phone transmit circuit. Similarly, in order for the headset adapter to receive and process a receive signal transferred from the host phone, the headset adapter receive lines must be matched with the two wires of the host phone handset jack corresponding to the host phone receive circuit.
In addition, different host phones may utilize transmit circuits of varying sensitivities. The headset adapter must provide a transmit signal gain adjustment to prevent the output from the headset adapter being too low or too high on the microphone transmit lines. Similarly, different host phones may utilize receive circuits which output a receive signal at varying gain levels. The headset adapter must provide a receive signal gain adjustment to prevent overloading of the headset adapter receive circuit or outputting a receive signal to the headset speaker at too high of a volume for the user.
However, because the handset jack wiring, host phone transmit circuit sensitivity, or host phone receive circuit output is not known in advance by the headset adapter manufacturer, various wiring configuration settings, transmit signal gain settings, and receive signal gain settings need to be provided on the headset adapter unit. In the prior art, these settings have been performed manually by the user. For example, the user must test different wiring configurations to match the transmit lines and receive lines of the headset adapter with the corresponding lines of the host phone handset jack. Once the wiring is correctly set, the user must make a test call and adjust the transmit sensitivity until the far end caller can hear properly. The user must also adjust the receive sensitivity so that the output at the headset speaker is at a comfortable level. This requires the user to perform a set up sequence whereby they try different settings, make test calls and subjectively judge when a configuration is optimally set.
Furthermore, with the introduction of digital signal processing and the inherent latency associated with such technology, additional problems with delayed sidetone have required the use of echo cancellers to remove the sidetone generated in the host phone. The rules governing the convergence of the adaptive filters in such echo cancellers can prevent the convergence if the configuration gains are not accurately set. This is because the sidetone level must be significantly less than the incoming receive signal level for the double-talk detector to allow the echo canceller to converge. If the host phone has high sidetone, or if the user has set the transmit gain too high, the echo canceller will not work.
In the prior art, there have been attempts at auto configuration of headset adapters which have involved passing tones through the host phone sidetone path and attempting to recognize and measure the level of the returning signal. The controller would then cycle through the switch options, take measurements on each and try to judge the best setting. Frequently, multiple settings would give erroneous signal levels due to hum and buzz or cross-coupled circuits and the controller would pick the wrong setting, forcing the user to manually set up the adapter. These techniques require the user to physically put the unit into a “learn mode” which is not intuitive and may be inadvertently omitted by the user if instructions accompanying the headset are not read. U.S. Pat. No. 5,729,603 titled “Self-Configuring Telephone Interface Unit” and also assigned to the present applicant Plantronics, Inc., discloses the use of a test dial tone in the auto configuration process.
Another prior art method used a measurement of the host phone microphone bias voltage and current to determine what kind of microphone was being used in the handset and set the gains accordingly. This solution is only partially successful as the range of microphone sensitivities for a particular type was too great and the gain still required user intervention in order to optimize.
While these solutions work to varying extents, they may be difficult for a user to operate. This introduces complexity for the user in setting the unit up to work properly with their phone. As a result, for these and other reasons, there is a need for improved methods and apparatuses for headset adapter circuits.